Debugger::_exceptionHandler sends header ContentType: text/html; charset=utf-8
Debugger::_exceptionHandler tries to log errors occurred while processing errors
Debugger::enable(): exit() replaced with _exceptionHandler()
Debugger::enable() checks whether log directory exists and is absolute
Logger: throws exception when is unable to write to log file
error.phtml: fixed erasing of HTML output
Message "Unable to log error." is passed to error.html
Logger: for each type of error is created own 'error-sent' file [Closes #10]